Science of the Total Environment xxx (2011) xxx–xxx
STOTEN-12566; No of Pages 7
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Lead isotopes reveal different sources of lead in balsamic and other vinegars
Kuria Ndung'u a,⁎, Sharon Hibdon b, Alain Véron c, A. Russell Flegal b
a Department of Applied Environmental Science (ITM), Stockholm University, S-106 91, Stockholm, Swedenb Environmental Toxicology, WIGS, University of California, Santa Cruz, CA 95064, USAc CEREGE, CNRS U.M.R. 6635, Université Aix-Marseille 3, B.P. 80, 13545 Aix en, Provence Cedex 4, France
⁎ Corresponding author at: Department of AppliedStockholmUniversity, Svante Arrhenius Väg 8, SE-106 9186747236; fax: +46 86747636.
Please cite this article as: Ndung'u K, et al,(2011), doi:10.1016/j.scitotenv.2011.04.001
a b s t r a c t
a r t i c l e i n f o
Article history:Received 15 February 2011Received in revised form 1 April 2011Accepted 1 April 2011Available online xxxx
Keywords:Pollutant lead (Pb)Stable lead isotopesBalsamic vinegarHR-ICP-MSMC–ICP-MSFood contamination
Fifty-eight brands of balsamic vinegars were analyzed for lead concentrations and isotopic compositions(204Pb, 206Pb, 207Pb, and 208Pb) to test the findings of a previous study indicating relatively high levels of leadcontamination in some of those vinegars — more than two thirds (70%) of them exceeded California's StateMaximum Level (34 μg/L) based on consumption rates≥0.5 μg Pb per day. The Lead isotopic fingerprints of allthose vinegars with high lead concentrations were then found to be primarily anthropogenic. This isotopicanalysis unquestionably reveals multiple contamination sources including atmospheric pollutant Pb and anunidentified contamination source, likely occurring after grape harvest. Organically grown grape vinegarsdisplay the same Pb content and isotopic signatures as other vinegars. This implies that pesticides might notbe a significant source of pollutant Pb in vinegars. A significant post-harvest contamination would beinherited from chemicals added during production and/or material used during transport, processing orstorage of these vinegars. This is consistent with the highest Pb levels being found in aged vinegars(112±112 μg/L) in contrast to other vinegars (41.6±28.9 μg/L) suggesting contamination during storage. Itis, therefore, projected that lead levels in most vinegars, especially aged balsamic and wine vinegars, willdecrease with improvements in their manufacture and storage processes consequential to recent concernsof elevated levels of lead in some vinegars.
Lead is a principal environmental and industrial pollutant,currently ranked second only to arsenic in the US Agency for ToxicSubstances and Disease Registry's priority List of Hazardous Sub-stances (http://www.atsdr.cdc.gov/cercla/07list.html) based on itsfrequency, toxicity, and potential for human exposure. This ranking isdue, in part, to the legacy of industrial lead emissions accumulated inenvironmental reservoirs (Murozumi et al., 1969; Shiharata et al.,1980; Flegal and Patterson, 1983; Véron et al., 1987; Nriagu andPacyna, 1988). As a consequence of those historic and contemporaryemissions of industrial lead, as well as variations of natural lead in theenvironment, lead concentrations in foods can vary widely (Dabekaand McKenzie, 1987; Flegal et al., 1990; Lee et al., 1991; Bolger et al.,1996; Rosman et al., 1998; Gulson et al., 1998; Scelfo and Flegal, 2000;Stockley et al., 2003; Rankin et al., 2005). Dietary exposure to Pb hassignificantly decreased over the past 30 years with the phasing out ofleaded gasoline, elimination of lead-soldered cans, and reductions inother sources of industrial lead contamination (Nriagu, 1990;
Thomas et al., 1999). Despite these reductions, the lead content ofhuman blood (PbB) is still 10–100 times above its estimated naturallevel of 0.016 μg/dL (Flegal and Smith, 1992; Smith and Flegal, 1992).
Fortunately, sources of natural and industrial lead in PbB and foodscan be distinguished by their isotopic ratios (Rabinowitz et al., 1973;Yaffe et al., 1983; Keinonen, 1992; Gulson et al. 1992; Gulson andWilson, 1994; Angle et al., 1995; Rankin et al., 2005; Gulson et al.,2006; Gulson, 2008). Lead has four stable isotopes (204Pb, 206Pb, 207Pb,and 208Pb), with the last three being end-members of the naturaluranium (U)–thorium (Th) decay series. Ratios of these stableisotopes vary according to the age of ore bodies or crustal mineralsand its initial U–Th content (Doe, 1970). Because there is no physical,chemical or biological fractionation of lead isotopes, their isotopicratios can be used to distinguish natural and industrial inputs of leadto the biosphere (Flegal and Smith, 1995). For example, lead isotopicmeasurements have been used to identify the origins of lead in winesduring production and storage (Lee et al., 1991; Gulson et al., 1992;Augagneur et al., 1997; Rosman et al., 1998; Almeida and Vasconcelos,1999, 2003; Medina et al., 2000; Barbaste et al., 2001; Larcher et al.,2003; Stockley et al., 2003; Mihaljevic et al., 2006).
Those isotopic analyses of lead inwines directly relate to our interestin the sources of another grape product: vinegars. This interest resultedfrom our efforts to accurately measure lead concentrations in differenttypes of vinegar (Ndung'u et al., 2004). In the process, we observedpronounced variations in the lead concentrations within certain brands
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of vinegar and between types of vinegars. Those differences attested tothe presence of relatively high levels of contaminant lead in at leastsomeof the vinegars (notably balsamic vinegars), raising thequestion ofwhat were the sources of that contamination. Therefore, the followingisotopic compositions were measured to supplement our previousconcentration measurements and determine whether it would bepossible to identify or at least characterize the sources of lead in morethan seventy (70) different types of vinegar. These included fifty-eight(58) brands of balsamic vinegar (including five (5) organic and one (1)rice vinegars), nine (9) brands of wine vinegar and one brand each of,apple cider, malt, and cognac vinegars.
2. Materials and methods
2.1. Samples
We have measured the lead isotopic composition of 205 vinegars(Table 1). The emphasis on balsamic vinegars was based on ourprevious analyses, which indicated they tended to have the highestlead concentrations. To determine the variability of lead concentra-tions within individual brands, replicate samples (n=4 to 7) ofdifferent brands, including at least one brand of each of the threetypes of vinegar (apple cider, wine, and balsamic), were collected.Most of the vinegars were in glass bottles; a few were in plastic orceramic bottles.
All of the vinegars were purchased by an independent party fromretail stores in central California. The samples were then transportedto the University of California, Santa Cruz (UCSC). The vinegars weretransferred to our care with a chain of custody and stored in a HEPA(Class 1000) filtered air, trace metal clean laboratory. The sampleswere then processed for analyses of their lead concentration andisotopic composition within a HEPA (Class 100) filtered air, laminarflow hood within that laboratory.
2.2. Reagents
All solutions and reagents were trace metal grade (TMG) or better(e.g., 2x sub-boiling quartz distilled). This included high purity (18 MΩcm) water (Milli-Q) that had been deionized and filtered before it waspassed through an analytical reagent-grade water purification system(Millipore, Bedford, MA). Calibration standards for lead concentrationmeasurements were made with a commercial standard solution (SpexPlasma, Edison, NJ). Concentrated HNO3 and HCl (Fisher Scientific,Pittsburgh, PA) were used for cleaning laboratory ware. Optima® grade(Fisher) HNO3was used in preparation of calibration standard solutionsand analytical solutions. 30% H2O2 (Ultrapur, Bayer, Pittsburg, NJ) andOptima® grade concentratedHNO3 (Fisher)were used in the digestionsand subsequent UV oxidations of the samples. The amount ofcontaminant lead in the TMG H2O2 added to vinegars (ca. 1% afterdilution) was less than the analytical uncertainty of the measurements.The matrix modifier used in the graphite furnace atomic absorptionspectrometry (GFAAS) analyses contained 0.05 mg NH4H2PO4 and0.003 mg Mg(NO3)2 per 5 μL solution (Environmental Express, Mt.Pleasant, SC). Additional details are provided in Ndung'u et al. (2004).
2.3. Analyses
Lead concentrations were initially measured by GFAAS, as detailedin Ndung'u et al. (2004). These analyses were made with a PerkinElmer SIMAA 6000, equipped with a Zeeman background correctorand AS72 auto sampler using end capped, traversely-heated andpyrocoated graphite tubes with an integrated L'vov platform. A leadelectrodeless discharge lamp (Perkin Elmer) was set at the recom-mended wavelength (283.3 nm) and lamp current (450 mA). Mag-nesium nitrate/ammonium phosphate [Mg(NO3)2/NH4H2PO4] wasused as the chemical modifier.
Please cite this article as: Ndung'u K, et al, Lead isotopes reveal differe(2011), doi:10.1016/j.scitotenv.2011.04.001
The GFAAS analyses of lead concentrations were intercalibratedwith measurements by magnetic sector, high resolution inductivelycoupled plasma mass spectrometry (HR ICP-MS), using protocolsdetailed by Ndung'u et al. (2004). The analyses were made with aThermo-Finnegan Element-1 instrument fitted with a Glass Expan-sion Conikal nebulizer, Scott-type double pass spray chamber (cooledto 10 °C), and standard nickel cones. Since no measurable polyatomicinterferences were found, lead concentrations were measured at lowresolution (r=300) using 209Bi as the internal standard.
Lead isotopic compositions of all of the sampleswere thenmeasuredwith multiple, replicate analyses by HR ICP-MS, using the sameinstrumental protocols. To enhance the accuracy and precision ofthose initial isotopic analyses, we purified and concentrated aliquots ofsome of those samples by passing them through an anion exchangeresin (AG 1X8), using procedures detailed by (Rankin et al., 2005). Leadisotopic compositions of those aliquots weremeasuredwith a FinneganMAT Neptune magnetic sector, multiple collector, high resolutioninductively coupled plasma mass spectrometer (MC ICP-MS) with anApex HF sample introduction system (Elemental Scientific Inc.) in aHEPA (Class 1000) filtered air, tracemetal clean room, using establishedprocedures (Gallon et al., 2008). The sensitivity of the MC ICP-MSmeasurements was 5.5 V for 208Pb at 100 ng/g Pb. Measured isotopicratios were corrected for mass bias using thallium additions with anexponential function (205Tl/203Tl=2.3888). Counts of 204Pb werecorrected on line for isobaric interferences from 204Hg by monitoring202Hg, with the assumption that the ratio of its natural abundance(204Hg/202Hg) was 0.2298. The measurements were calibrated withconcurrent analyses of 20 ppb of National Institute of Standards andTechnology (NIST)StandardReferenceMaterial (SRM) for common lead(981). Procedural blanks, including column extraction blanks, wereprocessed and analyzed concurrently. Corrections for 204Pb/206Pb,207Pb/206Pb, and 208Pb/206Pb averaged 0.0003, +0.003, and +0.009,respectively.
There were no significant (pb0.05) differences between Pbisotopic compositions measured by HR ICP-MS and MC ICP-MS. Thecorrelation (R2=0.9612, simple linear regression) of the 206Pb/207Pbratios of samples measured by both HR ICP-MS and MC ICP-MS washighly significant (Pb0.01), with a slope (y) of 0.9201 and anintercept of 0.0951. Based on this intercalibration, we determined thatthe complete data set obtained from the HR ICP-MS analyses could beused to investigate the sources of lead in the vinegars.
3. Results and discussion
3.1. Environmental or industrial contamination?
3.1.1. Pb concentrationsLead concentrations of all the vinegars are listed in Table 1, along
with the vinegar type, country of origin, and period of aging (whenavailable). Lead concentrations of the same vinegar brand usuallyvary b10%, which is consistent with analytical precision of concen-tration measurements at that level, with the exception of a fewsamples with relatively high lead concentrations. The range in leadconcentrations of individual samples extend from a low of 3.8 μg/L inone bottle of apple cider vinegar to a high 627 μg/L in one agedItalian balsamic vinegar (Table 1). Because of its cost ($175 for100 mL), only one bottle of that aged balsamic vinegar was pur-chased for this study. We, therefore, processed and analyzed multiplesub-samples of that vinegar to establish the reproducibility of its leadconcentration (627±39 μg/L). In general, a large fraction (70%) of allthe vinegars (most particularly balsamic brands) had lead concen-trations ≥34 μg/L, which exceeded California's State Maximum Level(SML) for human consumption (0.5 μg Pb per day). An aged Frenchwine vinegar shows the second highest concentration (594 μg/L),while lead concentrations of the cognac, garlic, apple cider, and ricevinegars are all below the SML (Fig. 1, Table 1).
nt sources of lead in balsamic and other vinegars, Sci Total Environ
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Please cite this article as: Ndung'u K, et al, Lead isotopes reveal different sources of lead in balsamic and other vinegars, Sci Total Environ(2011), doi:10.1016/j.scitotenv.2011.04.001
The vinegars analyzed include; balsamic (BV), wine (WV), cognac (CV), malt (MV), andapple cider (AV). Organic and rice balsamic vinegars are referred as “BV org” and “BVR”respectively; wine garlic vinegar is noted “WV gar”. Analyses of different bottles for thesame brand are numbered BV-, WV-, CV- or AC-2 to 7; replicate analyses from the samebottle are indicated as BV-d (1 to 9). The country of origin is indicated when known(otherwise noted “NI” for “not indicated”). “ND” in the analytical columns stands for“not determined”. Aged vinegars are listed as “aged” with the duration of aging (ifindicated on the bottle label).
4 K. Ndung'u et al. / Science of the Total Environment xxx (2011) xxx–xxx
Please cite this article as: Ndung'u K, et al, Lead isotopes reveal differe(2011), doi:10.1016/j.scitotenv.2011.04.001
In order to investigate the role of aging on the accumulation ofpollutant lead, we have compared lead concentrations between knownaged vinegars and the others. The mean lead concentrations in agedvinegars (112±112 μg/L) and other vinegars (41.6±28.9 μg/L) aresignificantly different (pb0.05, Student's t-test) suggesting thatelevated lead concentrations in balsamic vinegars could be explainedfor themost part by industrial (post-harvest), rather than environmen-tal (pre-harvest), contamination.
3.1.2. Isotopic imprint of balsamic vinegarsLead isotopic ratios of the vinegars are listed in Table 1. As
previously noted, variation of lead concentrations of the same vinegarare consistent with analytical precision of concentrations at that level.In contrast, lead isotopic ratios of the same vinegar brand generallydisplay significant variations that generally exceed 0.3%, an order ofmagnitude larger than the analytical uncertainty of HR ICP-MSmeasurements.
The lead isotopic compositions of balsamic vinegars are shownin Fig. 2, along with those of (1) uncontaminated environmentsrepresented by pre-industrial Mediterranean soils and sediments(end-member A) and (2) pollutant aerosols in Northern Italy (end-member B), which were collected in Florence and Venice (Bollhofer
Fig. 2. Isotope imprints of balsamic vinegar sorted according to Pb concentration (belowCalifornia's State Maximum Level (SML): gray circles; between SML and 100 μg/L: opencircles; above 100 μg/L: closed circles) and compared to (1) non-contaminatedMediterranean soils (Erel et al., 1997; Miralles et al., 2004; Teutsch et al., 2001; Vilometet al., 2003) and sediments (Marin 1998; Ferrand et al., 1999;Miralles et al., 2006) (crosses,end-member A) and (2)mid 1990s atmospheric pollutant Pb imprints fromNorthern Italy(Bollhofer and Rosman 2001; Tommasini et al., 2000) (end-member B).
nt sources of lead in balsamic and other vinegars, Sci Total Environ
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and Rosman, 2001; Tommasini et al., 2000). End-member B is basedon the assumption that most grapes used for Italian balsamic vinegaroriginate from the Emiliana–Romagna region where balsamic vinegaris produced. We hypothesize that the isotopic composition of thevinegars shall fall between the signature of natural sediments and theimprint of industrial aerosols (as deposited into top soils and grapes)in the production area. However, the isotopic composition of balsamicvinegars reveals another radiogenic end-member (C) that is clearlydifferent from the non-contaminated end-member (A) and appearsto represent another source of lead contamination. This end member(C) may represent a suite of contaminant sources with isotopiccompositions between those of the other two end-members.
Our isotopic analysis reveals (1)multiple sources of pollutant lead inbalsamic vinegars and (2) the relative insignificant role of “crustal” Pbfrom soils (end-member A) in those vinegars, with relatively high leadconcentrations. It is very clear that environmentally derived contami-nant lead (end-member B) cannot solely account for the elevated leadlevels in those vinegars, indicating an additional contribution fromanother pollutant source. This could be from contamination duringprocessing, storage, and/or theadditionofothermaterials (e.g.,flavoringand coloring).Wine vinegars also tend to have isotopic trends similar tothose of the balsamic vinegars (Fig. 2), which are subsequentlyaddressed in terms of regional isotopic compositions of their origins.
There is no clear groupingof isotopic ratios relative to concentrationsin balsamic vinegars. This disparity substantiates the hypothesizedpresence of multiple sources of lead contamination, which is furtherindicated by a plot of 206Pb/207Pb ratios vs. 1/Pb for balsamic vinegars(Fig. 3). When statistically reliable, the extrapolation of 1/Pb toward0 provides the isotopic signature of the source of contamination,assuming it is a single sourcewith a constant isotopic composition.Here,the coefficient correlation for the curve fit is not statistically significant(r2=0.1) owing to the large variance of the data, suggesting multiplesources of pollutant lead in these vinegars.
Oneof those additional sources of contamination could be associatedwith the use of pesticides (e.g., lead arsenates). These pesticides havebeen sprayed on some vineyards for pest control (Handson, 1984) andhave been found as a source for lead in some wines (Crecelius, 1977).Isotopic compositions of organically grown balsamic vinegars –with noadded pesticides – are very similar to those of other Italian balsamicvinegars implying that pesticides do not contribute significantly to thecontamination of balsamic vinegars (Table 1). Moreover, aged organicvinegars show elevated lead concentrations (PbN80 μg/L, 50BV, 17BVand 8BV) compared to those of other organically grown vinegars(Pbb50 μg/L), further attesting to the post-harvest introduction ofadditional lead contamination.
1.15
1.16
1.17
1.18
1.19
1.20
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
1/Pb
206Pb/207Pb
r2 = 0.1
Fig. 3. Possible isotopic signature of pollutant Pb sources in balsamic vinegar determinedfrom 206Pb/207Pb ratios vs. 1/Pb.
Please cite this article as: Ndung'u K, et al, Lead isotopes reveal differe(2011), doi:10.1016/j.scitotenv.2011.04.001
In summary, our analyses show that (1) relatively small amountsof natural lead accumulate in balsamic vinegars, (2) contributionsfrom pesticides are minimal, and (3) there are multiple sources ofpost-harvest anthropogenic lead in the vinegars we analyzed.
Based on lead concentration differences between aged and non-aged vinegars and their isotopic ratios (Fig. 2), we propose that post-harvest contamination accounts for at least half (≥50%) of the lead inbalsamic vinegars. This is consistent with recent observations byAlmeida and Vasconcelos (2003) and Rosman et al. (1998), who showthat lead concentrations of wine increase during post-harvestprocessing and that no more than a third of lead contamination inthose wines is derived from atmospheric deposition on the grapes orthe soil they are grown in. Similarly, PbIC investigations of variousstages in the wine making process for red and white wines showedsignificant post harvest introduction of lead, the source of which wasnot always obvious (Stockley et al., 2003).
3.1.3. Other vinegarsThe few Spanish and French vinegars analyzed as part of this
investigation also reveal the presence of anthropogenic post-harvestlead contamination. None of their isotopic compositions correlatewith their presumed regional exposure to industrial lead aerosols(Fig. 4). This disparity is, again, consistent with those observed inprevious isotopic composition analyses of French wines, which werefound to be significantly different from those of soils they were grownin (Augagneur et al., 1997; Rosman et al., 1998; Barbaste et al., 2001).Moreover, the isotopic compositions of those French wines are similarto those of the French vinegars included in this study (Table 1).
The sources of lead in Californian vinegars cannot be readilyresolved. Lead isotopic compositions of most US vinegars analyzed areclose to or within the range of those of environmental lead con-tamination as defined from aerosol signatures (Fig. 4). This implies thatvinegars produced in California are either more contaminated byenvironmentally derived industrial lead (pre-harvest contamination)and/or that this US environmental isotopic imprint and that of potentialindustrial sources associated with the production of vinegars (post-harvest contamination) do overlap. However, the large range of isotopicsignatures (e.g., 206Pb/207Pb varies from 1.168 to 1.202 for the fourvinegarsmade in California, i.e. 1AV, 1WV, 2WVand12BV; Table 1)maysuggest multiple pollutant sources.
The multiplicity of contaminant sources is also evidenced by theplot of 206Pb/207Pb ratios vs. 1/Pb for brands with lead concentrationsthat vary by a factor of 2 or more (Fig. 5). This includes a Californianorganic apple cider vinegar (1AV), along with two French vinegar
2.38
2.40
2.42
2.44
2.46
1.08 1.11 1.14 1.17 1.20 1.23
Italian vinegarFrench vinegarUS vinegarSpanish vinegar
206Pb/207Pb
N. Italy
Spain
S. France
US
208Pb/207Pb
Fig. 4. Isotopic imprints of Italian (gray closed circles), French (opened circles), US(dark closed circles), and Spanish (opened squares) vinegars and correspondingcontaminated atmospheric signatures (Alleman, 1997; Bollhofer and Rosman, 2001;Erel et al., 2007; Grousset et al., 1994; Hopper et al., 1991; Marcantonio et al., 2002; Roy,1996; Veron et al., 1992, 1999; Veron and Church, 1997).
nt sources of lead in balsamic and other vinegars, Sci Total Environ
5W wine vinegar1CV cognac vinegar1AV apple cider vinegar
206Pb/207Pb
1/Pb
r2= 0.9
r2= 0.8
Fig. 5. 206Pb/207Pb ratios vs. 1/Pb plots for two French vinegars (5WV and 1CV) and oneCalifornian vinegar (1AV) showing the largest concentration variance (up to 50%) for(n=7) sample analyses within the same brand.
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brands (wine vinegar 5WV and cognac vinegar 1CV). The apple cidervinegar has the lowest mean lead concentration (5.4±1.6 μg/L) of allthe analyzed brands of vinegar while one of those French vinegars(5WV) has the second largest mean concentration (237±223 μg/L).The other French cognac vinegar (1CV) has an intermediatemean leadconcentration (13.7±5.2 μg/L). Although French vinegars havesimilar geographic origins, their isotopic ratios are distributed alongdifferent mixing lines (Fig. 5); there is even a greater isotopiccomposition disparity for the California vinegar, which has twodifferent mixing lines for the same brand. These divergences providefurther evidence for multiple contamination sources and corroboratethe assumption of likely overlapping isotopic source signaturesfor environmental and industrial pollutant lead in California andelsewhere.
4. Conclusions
Vinegar lead isotopic imprints corroborate previous lead concen-tration analyses indicating pervasive industrial lead contamination ofvinegars sold in California (Ndung'u et al., 2004). These include ~70%of the 58 brands of balsamic vinegar with lead concentrationsexceeding 34 μg/L, the California State Maximum Level based onhuman consumption of≥0.5 μg Pb per day. The isotopic compositionsof all of the vinegars attest to the presence of lead contamination,often well above that of natural lead. Sources of lead contamination inthose vinegars include pre-harvest inputs (e.g., from atmosphericdeposition on grapes and soil) and post-harvest inputs (e.g., industrialprocessing and storage of vinegars). We estimate that this industrialpost-harvest input constitutes a significant fraction (N50%) of the totallead contamination in aged balsamic vinegars. It is expected that leadconcentrations in those vinegars will now decrease not only inresponse to the reduction in atmospheric emissions of pollutant leadbut mostly owing to efforts to minimize lead contamination ofvinegars during their production and storage prompted by thisinvestigation and other similar studies on wine (Almeida andVasconcelos, 2003). An investigation of lead concentration andassociated isotopic imprints in grapes and corresponding industrialproducts/materials during vinegar production, similar to the Stockleyet al. (2003) investigations, would complete our findings and helpreveal the source(s) for industrial lead contamination.
Please cite this article as: Ndung'u K, et al, Lead isotopes reveal differe(2011), doi:10.1016/j.scitotenv.2011.04.001
Acknowledgments
Rob Franks and several members of the WIGS laboratory wereinstrumental in various aspects of the study. This study was funded, inpart, by the Environmental Law Foundation (ELF). The ELF did nothave a role in the design collection, analysis and interpretation ofdata; in the writing of this study; and in the decision to submit thepaper for publication.
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